1. Technical Field
This invention relates generally to the planarization of semiconductor substrates and, more particularly to the conditioning of polishing pads in slurry-type polishers.
2. Background Information
Integrated circuits are typically formed on substrates, particularly silicon wafers, by the sequential deposition of conductive, semiconductive or insulative layers. After each layer is deposited, the layer is etched to create circuitry features. As a series of layers are sequentially deposited and etched, the outer or uppermost surface of the substrate, i.e., the exposed surface of the substrate, becomes successively less planar. This non-planar outer surface presents a problem for the integrated circuit manufacturer as a non-planar surface can prevent proper focusing of the photolithography apparatus. Therefore, there is a need to periodically planarize the substrate surface to provide a planar surface. Planarization, in effect, polishes away a non-planar, outer surface, whether a conductive, semiconductive, or insulative layer, to form a relatively flat, smooth surface.
Chemical mechanical polishing is one accepted method of planarization. This planarization method typically requires that the substrate be mounted on a carrier or polishing head, with the surface of the substrate to be polished exposed. The substrate is then placed against a rotating polishing pad. The carrier head may also rotate and/or oscillate to provide additional motion between the substrate and polishing surface. Further, a polishing slurry, including an abrasive and at least one chemically-reactive agent, may be spread on the polishing pad to provide an abrasive chemical solution at the interface between the pad and substrate.
Important factors in the chemical mechanical polishing process are: substrate surface planarity and uniformity, and the polishing rate. Inadequate planarity and uniformity can produce substrate defects. The polishing rate sets the time needed to polish a layer. Thus, it sets the maximum throughput of the polishing apparatus.
It is important to take appropriate steps to counteract any deteriorative factors which either present the possibility of damaging the substrate (such as by scratches resulting from accumulated debris in the pad) or reduce polishing speed and efficiency (such as results from glazing of the pad surface after extensive use). The problems associated with scratching the substrate surface are self-evident. The more general pad deterioration problems both decrease polishing efficiency, which increases cost, and create difficulties in maintaining consistent operation from substrate to substrate as the pad decays.
The glazing phenomenon is a complex combination of contamination, thermal, chemical and mechanical damage to the pad material. When the polisher is in operation, the pad is subject to compression, shear and friction producing heat and wear. Slurry and abraded material from the wafer and pad are pressed into the pores of the pad material and the material itself becomes matted and even partially fused. These effects reduce the pad""s roughness and its ability to apply fresh slurry to the substrate.
It is, therefore, desirable to continually condition the pad by removing trapped slurry, and unmatting or re-expanding the pad material.
A number of conditioning procedures and apparatus have been developed. Common are mechanical methods wherein an abrasive material is placed in contact with the moving polishing pad. For example, a diamond coated screen or bar may be used which scrapes and abrades the pad surface, and both removes the contaminated slurry trapped in the pad pores and expands and re-roughens the pad.
In one aspect, the invention is directed to a conditioner head for conditioning the polishing surface of a polishing pad. The head includes a drive element carried for rotation about a longitudinal axis. The head further includes a disk backing element for carrying an abrasive disk and holding the lower surface of the disk in engagement with the polishing pad. A driven element couples the disk backing element to the drive element and transmits torque and rotation therebetween. The driven element is longitudinally movable between retracted and extended positions. An annular diaphragm spans a gap between the drive element and the driven element and is coupled to the drive element and the driven element so as to rotate therewith as a unit.
Implementations of the invention may include one or more of the following. The diaphragm may in part bound a pressure chamber which may be pressurized to shift the driven element from the retracted position to the extended position and depressurized to shift the driven element from the extended position to the retracted position. During transition between the retracted and extended positions a first surface of the diaphragm, exterior to the pressure chamber, rolls of a generally annular outer surface portion of the driven element traverses the gap and rolls onto a generally annular inner surface portion of the drive element.
The drive element may include a drive shaft and a collar substantially fixed to the drive shaft and having a generally annular inner surface portion. The driven element may include a drive sleeve encircling at least a length of the drive shaft and having a generally annular outer surface portion. The annular diaphragm may extend between an outer periphery and an inner aperture and may be sealingly secured along the outer periphery to the collar and along the inner aperture to the drive sleeve. The generally annular outer surface portion of the drive sleeve may be a circular cylinder and the generally annular inner surface portion of the collar may be a circular cylinder. The diaphragm may in part bound a pressure chamber. The pressure chamber may be pressurized to shift the drive sleeve from the retracted position to the extended position and depressurized to shift the drive sleeve from the extended position to the retracted position. During transition between the retracted and extended positions, a first surface of the diaphragm, exterior to the pressure chamber, may roll off the generally annular outer surface portion of the drive sleeve. The first surface of the diaphragm may then traverse a gap between the generally annular outer surface portion of the drive sleeve and the generally annular inner surface portion of the collar and roll onto the generally annular inner surface portion of the collar. A fluid for inflating the pressure chamber may be introduced to the pressure chamber through a channel in the drive shaft. The head may include a housing substantially rigidly coupled to a conditioner arm for moving the head at least transverse to the longitudinal axis. The housing may include a first portion encircling at least the length of the collar, which first portion is coupled to the collar by a bearing system for permitting the collar to rotate relative to the first portion about the longitudinal axis. A web may be formed at the upper end of the drive shaft, the collar depending from the web. A pulley may be substantially fixed to the web for transmitting torque to the drive shaft. The collar may comprise a first piece depending from and fixed to the web and a second piece, separately formed from the first piece. The second piece may engage the bearing system and the diaphragm may be secured along the outer periphery to the collar between the first and second pieces. The diaphragm may be partially sandwiched between an outer cylindrical surface of an annular lip depending from the first piece and a generally annular inner surface of the second piece which forms the generally annular inner surface portion of the collar.
In another aspect, the invention is directed to a disk holder for holding a conditioning disk for conditioning a polishing pad. The disk holding element has a lower face for engaging an upper surface of the conditioning disk. The disk holding element defines a plurality of generally radially outward extending channels along the upper surface of the conditioning disk.
Implementations of the invention may include one or more of the following. The disk may comprise a central region, an outer perimeter, a plurality of radially extending spokes, and a plurality of webs. The spokes may extend from the central region to the outer perimeter, each spoke having a lower surface for engaging the upper surface of the conditioning disk. The webs, one such web between each adjacent pair of spokes, may each have a lower surface at least partially vertically recessed from the lower surfaces of the adjacent spokes so as to define one channel. Each web may extend from the central region and terminate at an outboard edge, radially recessed from the outer perimeter. The outer perimeter may be formed as a rim having a plurality of radially extending passageways. Each passageway may be generally aligned with an associated channel for permitting flow radially outward through the passageway from the associated channel when the disk holding element and disk are rotated about a central longitudinal axis while at least a lower surface of the disk is exposed to a liquid. Each of the radially extending passageways may be formed as a downwardly extending recess in the rim. The conditioning disk may be readily securable to and removable from the disk holding element. Each spoke may carry a magnet for attracting the conditioning disk. The conditioning disk may be readily securable to and removable from the disk holder element and the disk holder element may be readily securable to and removable from a rotating fixture. Each spoke may carry a magnet for securing the conditioning disk to the disk holder element and for securing the disk holder element to the rotating fixture. A first pin may depend from a first spoke and a second pin may depend from a second spoke, the first and second pins receivable by the conditioning disk for preventing rotation of the conditioning disk relative to the disk holder element. The central region, outer perimeter, plurality of radially extending spokes, and plurality of webs may be unitarily formed as a single piece of material. Each spoke may have a relatively narrow section extending outward from the central region and joining a relatively wider section adjacent the outer perimeter. Each web may have an upper surface substantially coplanar with the upper surfaces of adjacent spokes.
In another aspect, the invention is directed to a disk holder element for holding a conditioning disk used in association with a conditioner head of an apparatus for conditioning the polishing surface of a polishing pad. The disk holder element includes a lower surface magnetically engageable with an upper surface of the disk and an upper surface magnetically engageable with a lower surface of the head. The disk holder element may comprise a plurality of magnets securing the disk to the disk holder element and securing the disk holder element to the conditioner head.
In another aspect, the invention is directed to a conditioner head for conditioning the polishing surface of the polishing pad. The head includes a generally circular abrasive disk having upper and lower surfaces. The lower surface defining a disk plane. A drive element is carried for rotation about a longitudinal axis. A disk backing element carries the disk and holds the lower surface of the disk in engagement with the polishing pad and applies force and torque to the disk. The disk backing element has an upper member, fixed to the drive element, which upper member has a central downward facing socket having a spherical surface portion. The disk backing element further includes a lower member, fixed to the abrasive disk, which lower membrane has a central upward facing projection with a spherical surface portion in sliding engagement with the spherical surface portion of the socket. The disk backing element further includes at least one resilient member, coupling the upper member to the lower member so as to bias the lower member toward a neutral orientation. In the neutral orientation the disk plane is perpendicular to longitudinal axis. The resilient member permits tilting of the disk plane relative to the longitudinal axis and permits transmission of torque and rotation from the drive element to the disk. The upper member may comprises a central hub. The at least one resilient member may comprise a plurality of radially extending spokes extending radially outward from the central hub. Each spoke may be upwardly and downwardly flexible for permitting tilting of the disk plane relative to the longitudinal axis while transmitting rotation from the drive element to the rim. The spherical surface portions of the socket and projection may have a common center lying substantially within the disk plane.
In another aspect, the invention is directed to a conditioner head for conditioning the polishing surface of a polishing pad using an abrasive conditioning disk. The conditioner includes a drive element carried for rotation about a longitudinal axis and a disk backing element for holding and applying torque to the abrasive conditioning disk. The disk backing element includes a central hub fixed to the drive element, an outer rim generally defining a rim plane, and a plurality of radially extending spokes. The spokes extend from the central hub to the outer rim. Each spoke is upwardly and downwardly flexible for permitting tilting of the rim plane relative to the longitudinal axis while transmitting rotation from the drive element to the rim. Each spoke may have a transversely extending wave for increasing the flexibility of the spoke. The spokes may be formed of steel. The head may further comprise a plate having a central upward facing projection having a spherical surface portion. The hub may have a central downward facing socket having a spherical surface portion in sliding engagement with the spherical surface portion of the projection.
In another aspect, the invention is directed to a process for conditioning a polishing pad. The process includes providing an abrasive conditioning disk carried by a disk carrier and having a lower surface engageable with a polishing surface of the polishing pad. The carrier is caused to rotate the conditioning disk and bring the lower surface of the conditioning disk into engagement with the polishing surface of the polishing pad. The carrier is caused to reciprocate in the path along the rotating polishing pad. A carrier is caused to disengage the conditioning disk form the polishing pad. The carrier is caused to rotate the conditioning disk and introduce the conditioning disk to a body of cleaning liquid so as to cause a flow of the cleaning liquid longitudinally upward from the lower surface of the conditioning disk, through the conditioning disk, and radially outward along an upper surface of the conditioning disk so as to clean the conditioning disk.
Implementations of the inventive process may include on or more of the following. A second liquid may be applied to the polishing surface of the polishing pad. The second liquid may be permitted to flow up through the lower surface of the conditioning disk, through the conditioning disk, and radially outward along the upper surface of the conditioning disk when the conditioning disk is engaged with the polishing surface of the polishing pad. The flow of the cleaning liquid along the upper surface of the conditioning disk may be through a plurality of generally radially outwardly extending channels defined by a disk holder.
Among the advantages which may be provided by the invention are improved sealing and reduced wear and particle generation. Since the diaphragm may be fixed at its inner aperture and outer periphery to the associated elements, it need not be in sliding engagement with those elements either during rotation or in translation of the end effector between retracted and extended positions. This lack of sliding engagement reduces wear and the associated particle generation between slidingly engaged surfaces and prevents contaminants from entering the pressure chamber between slidingly engaged surfaces.
Further advantages are provided by the end effector featuring a spoked flexure and spherical socket and projection joint. The joint permits the application of downward force from the head to the conditioning disk to maintain compression between the conditioning disk and polishing pad surface. The flexure transmits torque and rotation to the disk while permitting the disk plane to tilt relative to the axis of rotation allowing the disk to remain flat against the polishing pad during conditioning. The flexure may bias the disk into a neutral orientation with the disk plane substantially perpendicular to the axis of rotation. By forming the flexure with a plurality of thin flat spokes, a balance is achieved between the ability to transmit torque about the axis of rotation and the ability to flex to allow the disk plane to tilt relative to the axis of rotation. The sliding spherical surface joint, with a center of rotation located in the center of the lower surface of the disk, also allows for smooth tilting of the disk during operation.
Further advantages are provided by a disk holding element which defines a plurality of channels along the upper surface of the disk so that during conditioning of the pad or during rinsing of the disk, there is a flow of either slurry or cleaning fluid upward through the bottom surface of the disk, through the disk, and radially outward along the upper surface of the disk through the channels. The channels facilitate more efficient conditioning and cleaning of the disk.
A further advantage is provided by a disk holding element which is made readily removable from the backing element and from the disk. The holding element may first be secured to the disk and then the combined holding element and disk may be secured to the backing element. Alignment features on the disk holding element facilitate the precise registration of the disk and holder relative to the backing element without undue effort. To allow faster changeout and thus reduce downtime when a disk is replaced, while one disk is in the conditioning head, a fresh disk can be secured to a second disk holding element. The first disk and first holder may be removed from the head, and replaced with a second disk and second holding element and the conditioner restarted. The first disk may then be separated from the first disk holding element and the first disk holding element secured to a new disk to await subsequent use.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.